Which condition is characterized by elevated serum calcium and ALP?

The condition characterized by elevated serum calcium and alkaline phosphatase (ALP) levels is Paget's disease. In Paget's disease, there is a disruption in the normal process of bone remodeling, causing the affected bones to become enlarged and weakened. This abnormal bone turnover leads to increased osteoclast activity followed by compensatory osteoblast activity, which results in elevated levels of alkaline phosphatase, an enzyme associated with bone formation and remodeling.

Additionally, while primary hyperparathyroidism typically presents with elevated serum calcium, it does not usually elevate ALP levels significantly unless there is a concurrent bone disease such as osteitis fibrosa cystica. In secondary bone tumors, serum calcium can be normal or low due to bone being infiltrated, rather than being elevated. Osteoporosis characteristically does not show elevated serum calcium or ALP, as it is primarily a condition of decreased bone density without significant alterations in biochemical markers.

Thus, Paget's disease stands out as the condition where both serum calcium and ALP are markedly elevated due to the pathological increase in bone turnover.